Computer Science Course?

I'm thinking of taking a computer science course this year at school. In order to take it, I need to take either C++ or Java as a co-requisite. Which one would help out with the ap computer science course the most? Also I'm pretty sure that the computer science course would help me out in college (planning on mechanical engineering). Would it help? Thanks for the help. Sorry for the spelling and sorry if this is in the wrong forum

Oh and also can someone describe the differences between C++ and Java and the basics of what computer science will be about.